Electrodes, lithium-ion batteries, and methods of making and using same

ABSTRACT

Described herein are improved composite anodes and lithium-ion batteries made therefrom. Further described are methods of making and using the improved anodes and batteries. In general, the anodes include a porous composite having a plurality of agglomerated nanocomposites. At least one of the plurality of agglomerated nanocomposites is formed from a dendritic particle, which is a three-dimensional, randomly-ordered assembly of nanoparticles of an electrically conducting material and a plurality of discrete non-porous nanoparticles of a non-carbon Group 4A element or mixture thereof disposed on a surface of the dendritic particle. At least one nanocomposite of the plurality of agglomerated nanocomposites has at least a portion of its dendritic particle in electrical communication with at least a portion of a dendritic particle of an adjacent nanocomposite in the plurality of agglomerated nanocomposites.

PRIORITY CLAIM

The present application is a Continuation of U.S. patent applicationSer. No. 16/853,301, filed Apr. 20, 2020, which is a Continuation ofU.S. patent application Ser. No. 15/612,890, filed Jun. 2, 2017, whichis a Continuation of U.S. patent application Ser. No. 14/513,920, filedOct. 14, 2014, which is a Continuation of U.S. patent application Ser.No. 13/431,591, filed Mar. 27, 2012, which is a Continuation-in-part ofInternational Application No. PCT/US2010/050794, filed Sep. 29, 2010,which claims the benefit of U.S. Provisional Application No. 61/246,741,filed on Sep. 29, 2009.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with United States Government support under SBIRgrant number NNX09 CD29P 2008-1 awarded by the National Aeronautics andSpace Administration. The United States Government has certain rights inthis invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The various embodiments of the present invention relate generally toenergy storage devices, and more particularly, to lithium-ion batteries,and to methods of making and using such devices.

2. Description of the Relevant Art

Owing in part to their relatively high energy densities, light weight,and potential for long lifetimes, lithium-ion (Li-ion) batteries areused extensively in consumer electronics. In fact, Li-ion batteries haveessentially replaced nickel-cadmium and nickel-metal-hydride batteriesin many applications. Despite their increasing commercial prevalence,further development of Li-ion batteries is needed, particularly forpotential applications in low- or zero-emission hybrid-electrical orfully-electrical vehicles, energy-efficient cargo ships and locomotives,aerospace, and power grids. Such high-power applications will requireelectrodes with higher specific capacities than those used incurrently-existing Li-ion batteries.

Currently, carbon-based materials (e.g., graphite) are employed as thepredominant anode material in Li-ion batteries. Carbon (C), in the formof graphite, has a maximum or theoretical specific capacity of about 372milli-Ampere hours per gram (mAh/g), but suffers from significantcapacity losses during cycling.

Silicon-based materials have received great attention as anodecandidates because they exhibit specific capacities that are an order ofmagnitude greater than that of conventional graphite. For example,silicon (Si) has the highest theoretical specific capacity of all themetals, topping out at about 4200 mAh/g. Unfortunately, silicon suffersfrom its own significant setbacks.

The primary shortcoming of Si-based anode materials is the volumeexpansion and contraction that occurs as a result of lithium ionintercalation and deintercalation, respectively, during charge cyclingof the battery. In some cases, a silicon-based anode can exhibit anincrease, and subsequent decrease, in volume of up to about 400%. Thesehigh levels of strain experienced by the anode material can causeirreversible mechanical damage to the anode. Ultimately, this can leadto a loss of contact between the anode and an underlying currentcollector. Another shortcoming associated with Si-based anode materialsis their low electrical conductivity relative to carbon-based anodematerials.

The use of silicon-carbon composites to circumvent the limitations ofpure Si-based materials has been investigated. Such composites, whichhave been prepared by pyrolysis, mechanical mixing and milling, or somecombination thereof, generally include Si particles embedded in or on adense carbon matrix. The large volume changes in the Si particles uponlithium intercalation, however, can be accommodated by carbon only to alimited degree, thus offering only limited stability and capacityenhancements relative to pure Si-based anodes.

Thus, despite the advancements made in anode materials, Li-ion batteriesremain somewhat limited in their applications. Accordingly, thereremains a need for improved anodes for use in Li-ion batteries. Theseimproved anodes, and, ultimately, the improved Li-ion batteries, couldopen up new applications, such as the so-called high-power applicationscontemplated above. It is to the provision of such devices that thevarious embodiments of the present inventions are directed.

SUMMARY OF THE INVENTION

The various embodiments of the present invention provide improved Li-ionbattery components, improved Li-ion batteries made therefrom, andmethods of making and using such components and devices.

According to some embodiments of the present invention, an anodeincludes a porous composite comprising a plurality of agglomeratednanocomposites. At least one, and as many as all, of the plurality ofnanocomposites includes a dendritic particle formed from athree-dimensional, randomly-ordered assembly of nanoparticles of anelectrically conducting material (e.g., carbon, silicon, lithium-siliconalloys) and a plurality of discrete non-porous nanoparticles of anon-carbon Group 4A element or mixture thereof (i.e., silicon,germanium, tin, lead, and an alloy (e.g., lithium-silicon alloys) orsolid solution thereof) disposed on a surface of the dendritic particle.At least one nanocomposite of the plurality of agglomeratednanocomposites has at least a portion of its dendritic particle inelectrical communication with at least a portion of a dendritic particleof an adjacent nanocomposite in the plurality of agglomeratednanocomposites.

In some cases, the electrically conducting material of the dendriticparticle can be amorphous or graphitic carbon. For example, theamorphous carbon can be carbon black. The non-carbon Group 4A element ormixture thereof is silicon.

In certain situations, the porous composite also includes anelectrically conducting coating disposed on at least a portion of asurface of a dendritic particle of at least one of the plurality ofagglomerated nanocomposites. The electrically conducting coating can beformed from carbon, too.

It is possible for the plurality of agglomerated nanocomposites to beagglomerated together using an electrically conducting additive.Similarly, the electrically conducting additive can be carbon.

It is possible, in some embodiments, for at least a portion of thediscrete non-porous nanoparticles on the surface of the dendriticparticle to contact each other.

In certain embodiments, the plurality of discrete non-porousnanoparticles have an average longest dimension of about 5 nanometers toabout 500 nanometers.

The plurality of discrete non-porous nanoparticles can comprise about 15weight percent to about 90 weight percent of each nanocomposite.

The porous composite can be a spherical or substantially-sphericalgranule as desired.

A total pore volume within the porous composite can be at least about1.5 times a volume occupied by all of the nanoparticles in the porouscomposite. At the other end, the total pore volume within the porouscomposite can be less than about 20 times the volume occupied by all ofthe nanoparticles in the porous composite.

According to other embodiments of the present invention, an anode caninclude a matrix of a plurality of spherical or substantially-sphericalporous composite granules. At least one granule, and as many as all ofthe granules, in the plurality of granules comprises a plurality ofagglomerated nanocomposites. At least one nanocomposite of the pluralityof agglomerated nanocomposites includes a dendritic particle formed froma three-dimensional, randomly-ordered assembly of annealed carbon blacknanoparticles and a plurality of discrete non-porous siliconnanoparticles disposed on a surface of the dendritic particle. At leastone nanocomposite, and as many as all of the nanocomposites, has atleast a portion of its dendritic particle in electrical communicationwith at least a portion of a dendritic particle of an adjacentnanocomposite in the plurality of agglomerated nanocomposites.

A lithium ion battery can include any of the anodes described herein.

According to some embodiments of the present invention, a method ofmaking an anode can include forming a three-dimensional,randomly-ordered dendritic particle from a plurality of discretenanoparticles of an electrically conducting material. The method canalso include disposing a plurality of discrete non-porous nanoparticlesof a non-carbon Group 4A element or mixture thereof on a surface of thedendritic particle to form a nanocomposite particle. The method canfurther include assembling a plurality of nanocomposite particles toform a bulk unitary body or a spherical or substantially-sphericalgranule. Each nanocomposite particle of the plurality of nanocompositeparticles can have at least a portion of the dendritic particle inelectrical communication with at least a portion of a dendritic particleof an adjacent nanocomposite particle in the plurality of agglomeratednanocomposite particles.

In some cases, the method further includes assembling a plurality ofgranules to form an anode matrix, wherein at least a portion of at leastone nanocomposite particle of each granule has a dendritic particle inelectrical communication with a dendritic particle of at least a portionof at least one nanocomposite particle of an adjacent granule.

When the non-carbon Group 4A element or mixture thereof is silicon,disposing the plurality of discrete non-porous silicon nanoparticles caninvolve chemical vapor deposition of a decomposition product of a silaneor chlorosilane.

Assembling the plurality of nanocomposite particles to form the bulkunitary body or the spherical or substantially-spherical granule caninvolve granulation of the plurality of nanocomposite particles. Thegranulation step can include wet granulation using a polymeric binderthat is ultimately converted into carbon.

In some cases, the method further includes applying an electricallyconducting coating to at least a portion of the assembled plurality ofnanocomposite particles.

In some cases, the method also includes adding an electricallyconducting additive to enhance the electrical communication.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will become apparent to thoseskilled in the art with the benefit of the following detaileddescription of embodiments and upon reference to the accompanyingdrawings in which:

FIG. 1(a) is a schematic illustration of an exemplary nanocompositebuilding block for making an anode in accordance with some embodiments;

FIG. 1(b) is a schematic illustration of an exemplary granule for makingan anode in accordance with some embodiments;

FIG. 2 is a schematic illustration of an exemplary process for making ananode in accordance with some embodiments;

FIGS. 3(a) through 3(c) include transmission electron microscope (TEM)images obtained at different magnifications for a composite granule inaccordance with some embodiments;

FIG. 3(d) provides an EDX spectrum of a Si—C composite granule showingthe C and Si Kα lines, O and Cu sample holder lines;

FIG. 3(e) provides XRD spectra of Si-coated carbon black both before andafter carbon deposition at about 700° C. for about 30 minutes;

FIG. 3(f) provides a TEM image of a Si nanoparticle crystallized afterexposure to about 700° C.;

FIGS. 4(a) through (d) include scanning electron microscope (SEM) imagesrecorded at different magnification of the structure of a Si—C compositegranule self-assembled during carbon deposition on the Si-decoratedannealed carbon black particles;

FIG. 4(e) provides the cumulative size distribution of sphericalgranules synthesized at about 700° C.;

FIG. 4(f) illustrates N₂ sorption isotherms on the surface Si-decoratedannealed carbon black both before and after carbon chemical vapordeposition;

FIG. 4(g) provides Barrett-Joyner-Halenda cumulative specific surfacearea of Si-decorated annealed carbon black both before and after carbonchemical vapor deposition;

FIG. 4(h) provides high-magnification SEM images of the surface ofspherical granules produced during carbon-coating of pure carbon black,shown for comparison to FIG. 4(d);

FIG. 5(a) provides information regarding the electrochemical performanceof the Si—C granules as anodes in coin cell batteries taken at roomtemperature in two-electrode 2016 coin-type half-cells;

FIG. 5(b) illustrates the galvanostatic charge-discharge profiles of thegranule electrodes at rates of about C/20, 1 C and 8 C in comparison tothat of annealed carbon black- and commercial graphite-based electrodesbetween 0 and 1.1 V;

FIG. 5(c) illustrates differential capacity curves of the granuleelectrodes in the potential window of 0 to 1.1 V collected at the rateof 0.025 mV/s;

FIG. 5(d) provides a SEM image of a granule after electrochemicalcycling;

FIG. 6 graphically illustrates the size distribution of variousspherical granules synthesized at about 700 and about 730° C.; and

FIG. 7 provides reversible Li deintercalation capacity and Coulombicefficiency of an annealed carbon black electrode vs. cycle number incomparison to the theoretical capacity of graphite.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Thedrawings may not be to scale. It should be understood, however, that thedrawings and detailed description thereto are not intended to limit theinvention to the particular form disclosed, but to the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the present invention as definedby the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is to be understood the present invention is not limited toparticular devices or methods, which may, of course, vary. It is also tobe understood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting. As used in this specification and the appended claims, thesingular forms “a”, “an”, and “the” include singular and pluralreferents unless the content clearly dictates otherwise. Furthermore,the word “may” is used throughout this application in a permissive sense(i.e., having the potential to, being able to), not in a mandatory sense(i.e., must). The term “include,” and derivations thereof, mean“including, but not limited to.” The term “coupled” means directly orindirectly connected.

As stated above, the various embodiments of the present invention aredirected to improved anodes for use in Li-ion batteries, and Li-ionbatteries made therefrom. Methods of making and using the improvedanodes and batteries are also disclosed herein.

The improved anodes generally include composites of a non-carbon Group4A element or mixture thereof (e.g., silicon or lithium-silicon alloys)and an electrically conducting material (e.g., carbon). In contrast tothe prior art, however, the improved composite anodes described hereinare highly porous and can accommodate the significant volume changestypically caused by lithium alloying into the non-carbon Group 4Aelement or mixture thereof. As will be described in more detail below,pre-existing pores in the composite anodes provide sufficient volume forexpansion and allow for fast transport of lithium ions, while thepresence of an electrically conducting material allows for an improvedsolid/electrolyte interface formation, structural integrity, and highelectrical conductivity. As a result, the porous composite anodes canconserve their size and shape upon cycling, which is important forindustrial applications because commercial battery cells provide verylittle, if any, volume for anode expansion.

Structurally, the so-called “building blocks” of the anodes describedherein are individual nanocomposites, such as the one shown in FIG.1(a), which are formed from electrically conducting dendritic particlesthat have a plurality of discrete, non-porous nanoparticles of anon-carbon Group 4A element or mixture thereof disposed thereon.

As seen in FIG. 1(a), the nanocomposite 102 comprises a dendriticparticle 104, which itself is a three-dimensional, randomly-orderedassembly or agglomerate of nanoparticles (not individually shown) of anelectrically conducting material. The individual nanoparticles that formthe dendritic particle 104 generally have an average longest dimensionof about 5 nm to about 250 nm. As a result, the dendritic particle 104generally has a longest dimension of about 100 nanometers (nm) to about5 micrometers (n).

In exemplary embodiments, the electrically conducting material used toform the dendritic particle 104 is elemental carbon in one of itsamorphous (e.g., coal, soot, carbon black, or the like) or graphiticallotropes. In addition to elemental carbon, other electricallyconducting materials that are stable under the conditions to which theywill be exposed (i.e., they do not react with or substantiallysolubilize silicon during fabrication or use of the anode) can beimplemented. Such materials will be readily apparent to those skilled inthe art to which this disclosure pertains. By way of illustration,nickel is one such material.

Returning to the nanocomposites 102 in FIG. 1(a), disposed on thedendritic particle 104 is a plurality of discrete and non-porousnanoparticles 106 of silicon, tin (Sn), germanium (Ge), lead (Pb), or analloy or solid solution of Si, Sn, Ge, and/or Pb. Reference will now bemade to embodiments involving silicon as the non-carbon Group 4A elementfor illustrative convenience only.

Generally, the plurality of the discrete, non-porous siliconnanoparticles 106 can have an average longest dimension of about 5 nm toabout 200 nm. Since the native oxide that forms on the surface ofsilicon nanoparticles is about 0.5 nm to about 1 nm thick, particleswith an average longest dimension of about 1 nm to about 3 nm are toosmall to be used in the anodes of the present invention.

The plurality of silicon nanoparticles 106 can comprise about 15 weightpercent (wt. %) to about 90 wt. % of the nanocomposite 102, based on thetotal weight of the nanocomposite 102. In general, a lower siliconcontent results in better long-term stability of the anode, particularlywhen carbon is used as the electrically conducting material of thedendritic particle 104, because carbon can undergo a large number ofcharge/discharge cycles without failing. In contrast, when the siliconcontent is higher, the resulting anode will exhibit better gravimetriccapacity. Thus, in applications where long-term stability of the Li-ionbattery is more desired than a higher gravimetric capacity, thoseskilled in the art to which this disclosure pertains would appreciatethat lower silicon contents will be used. Similarly, in applicationswhere the capacity of the Li-ion battery is more important than thelong-term stability, higher silicon contents will be used to form thenanocomposite 102.

The anodes generally include a plurality of the nanocomposite buildingblocks 102 agglomerated or assembled together. As shown at the end ofthe process flow diagram in FIG. 2, these agglomerates or assemblies canbe in the form of a bulk unitary body 100 that adopts the ultimate shapeof the anode. Alternatively, these agglomerates can be in the form of aparticle or granule (e.g., the substantially spherical granule shown inFIG. 1(b) and designated by reference numeral 100), which can then bepacked together in close proximity with other such particles or granulesto form a matrix.

Each individual nanocomposite 102 within the agglomerate 100 isassembled in such a manner as to be in electrical communication with atleast one other nanocomposite building block 102. This is generallyaccomplished by having at least a portion of a surface of the dendriticparticle 104 of one nanocomposite 102 in contact with at least a portionof a surface of a dendritic particle 104 of another nanocomposite 102.In this manner, the conductivity of the anode is not unnecessarilydecreased by the surface resistance at nanocomposite-nanocompositeboundaries. Similarly, when the anode comprises a plurality ofagglomerated particles or granules 100, as shown in FIG. 1(b), theparticles or granules 100 are packed or arranged into a matrix in such amanner as to have each particle 100 be in electrical communication withat least one other particle 100.

It should be noted that, in embodiments where the silicon content of thenanocomposites 102 is high, it may be more difficult to ensure thatdendritic particles 100 of different nanocomposites 102 are insufficiently-high contact with one another. In such cases, theelectrical communication between individual nanocomposites 102 can beimproved by implementing an optional layer or coating of an electricallyconducting material (not shown) on at least a portion of thenanocomposites 102. This optional coating can be disposed directly onthe nanocomposites 102 before, during, or after the individualnanocomposites 102 are brought into sufficient proximity to one anotherto form the assembly or agglomerate 100. The electrically conductingmaterial of the optional coating can be the same or a different materialas the electrically conducting material of the dendritic particle 104.This optional coating can even be disposed directly on the siliconnanoparticles, but must be formed of a material, and have a thickness,that will enable lithium ions to diffuse therethrough. The optionalelectrically conducting coating can also serve to impede thedecomposition of the electrolyte, which results in the formation of thesolid-electrolyte interface (SET) layer.

Alternatively, instead of an electrically conducting coating or layer,an electrically conducting additive can be used to ensure that dendriticparticles 100 of different nanocomposites 102 are in sufficiently-highcontact with one another. One example of such an additive is an organicbinder that converts primarily to carbon during fabrication and prior toimplementation of the anode. Exemplary binders include polymericmaterials having at least about 20 atomic percent carbon in themonomeric unit used to form the polymer. Suitable polymers includepolyethers, polyesters, carbon homochain polymers, i.e., polyacrylates,polymethacrylates, polymers based on acrylonitrile, polymers based onvinylidene fluoride, and the like. Other additives for such purposes areknown to those skilled in the art to which this disclosure pertains.

As can be seen from the agglomerated nanocomposites 100 in FIGS. 1(b)and 2, regardless of how the nanocomposites 102 are assembled, the anodewill have a high level of porosity. The exact porosity of the anode,however, will depend on the silicon content of the individualnanocomposites 102. Generally, the available pore volume for siliconexpansion and contraction during charge cycling will be at least aboutthree times the volume of the silicon nanoparticles. This threshold porespace will minimize or completely prevent the anode from experiencingany strain as a result of the silicon expansion. In order to minimizeany adverse effects on the volumetric performance of the anode, the porevolume should be limited to less than or equal to about 20 times theoverall volume of the silicon nanoparticles. That is, when the porevolume is greater than about 20 times the volume of the siliconnanoparticles, the volumetric capacitance of the anode begins to suffer.

The anodes described above can be made using a variety of techniques.FIG. 2 provides a representative illustration of the general processesfor making an anode. As seen in the first step of the process flowdiagram of FIG. 2, these processes include forming a three-dimensional,randomly-ordered dendritic particle 104 from a plurality of discretenanoparticles of an electrically conducting material. Next, a pluralityof discrete non-porous silicon nanoparticles 106 are disposed on thedendritic particle to form a nanocomposite particle 102. Finally, aplurality of nanocomposite particles 102 are assembled together to forma bulk material 100 or a granule (shown in FIG. 1(b)) 100. In the lattercase, a plurality of the granules 100 can then be consolidated into amatrix that will serve as the anode.

The plurality of discrete nanoparticles of the electrically conductingmaterial can be assembled into the dendritic particle 104 in a number ofways. These include using a purely thermal treatment (e.g., sintering orannealing the particles together), sonication, chemically reacting thenanoparticles with one another, spontaneously (e.g., via a reduction inthe surface energy of adjacent nanoparticles), and/or the like. In oneembodiment, a carbon dendritic particle may be formed by annealingcarbon black particles at elevated temperatures (e.g., above 1800 C)which causes a portion of the particles to be fused/sintered together.In another embodiment, a dendritic particle may be formed by carbonizinga gaseous carbon precursor (e.g., a hydrocarbon gas) under conditionsthat promote the formation of dendritic carbon particles. Typicallypyrolysis of a hydrocarbon gas at 1 atm pressure and temperatures of 700C to 1400 C will promote dendritic particle formation. In a similarmanner, carbon dendritic particles may be formed by pyrolysis ofpolymeric particles.

Once the dendritic particle 104 is formed, the silicon nanoparticles 106can be disposed thereon. In some embodiments, the silicon nanoparticles106 can be grown directly on the surface of the dendritic particle 104.Many deposition techniques can be used to do this, including, withoutlimitation, physical vapor deposition and all of the variants thereof,chemical vapor deposition and all of the variants thereof, sputteringand all of the variants thereof, ablation deposition and all of thevariants thereof, molecular beam epitaxy and all of the variantsthereof, electrospray ionization and all of the variants thereof, andthe like. In other embodiments, the silicon nanoparticles 106 can beprepared independently, and then coupled to the surface of the dendriticparticle 104 using physical or chemical means.

In some embodiments the silicon nanoparticles 106 are discrete particlesso as to not form a continuous or substantially-continuous film on thesurface of the dendritic particle 104. By remaining as discreteparticles, silicon can expand and contract during charge cycling withminimal or no strain to the anode. In contrast, if the silicon weredisposed on the dendritic particle 104 as a continuous film or layer,there would be less pore space in the overall anode. This could resultin slower or less lithium ion movement into and out from the anodeduring charge cycling. It can also result in greater strain on the anodebecause significantly more of the anode could undergo expansion andcontraction during charge cycling.

In some embodiments, the silicon nanoparticles 106 are fully dense(i.e., less than or equal to about 5 percent of the surface of thenanoparticle comprises pore walls, based on the total surface area ofthe nanoparticle), rather than porous. Porosity in the silicon itselfcan result in lithium ions being trapped within the pore walls, therebycausing capacity losses for the anode.

Once the silicon nanoparticles 106 are disposed on the dendriticparticles 104 to form the nanocomposite building blocks 102, the overallanode structure can be formed. That is, a plurality of the nanocompositebuilding blocks 102 can be assembled together to form the anode. In somecases, the nanocomposite building blocks 102 can be assembled to form alarger particle or granule 100. Next, a plurality of granules can beconsolidated into a matrix, which will serve as the anode.Alternatively, the nanocomposite building blocks 102 can be assembled toform a bulk structure 100, which will serve as the anode.

The nanocomposite building blocks 102 can be aggregated using a varietyof techniques. These include the use of self assembly chemistry,pressure, heat, granulation, a binder, combinations thereof, or thelike.

If the optional electrically conducting coating is used, it can beimplemented after the nanocomposite building blocks 102 are produced,either before or during the step where the nanocomposite building blocks102 are aggregated. Alternatively, after the nanocomposite buildingblocks 102 are aggregated, the optional electrically conducting coatingcan be applied to the aggregated nanocomposite building blocks 102. Thiscoating can be applied to the nanocomposite building blocks 102 usingany of the techniques described above for growing the siliconnanoparticles 106.

If, however, the optional electrically conducting additive is used, itcan be incorporated during or after the step where the nanocompositebuilding blocks 102 are aggregated.

If the nanocomposite building blocks 102 are aggregated into granules orparticles 100, a plurality of granules or particles 100 can be placed inclose contact with one another to form a matrix, which can serve as theanode.

Once the anode is formed, it can be implemented in the fabrication of aLi-ion battery. Such a battery would include an anode as describedherein, a cathode, and an electrolyte separator, which is interposedbetween the anode and the cathode. Any type of Li-ion battery can beformed using the anodes described herein, as would be understood bythose skilled in the art to which this disclosure pertains.

During operation of the Li-ion battery, the battery cell can be chargedand discharged as would be understood by those skilled in the art towhich this disclosure pertains. By way of illustration, when the batteryis in use (i.e., discharging), lithium ions deintercalate from thesilicon nanoparticles 106 of the anode (causing the siliconnanoparticles 106 to contract), migrate through the ion-conductingelectrolyte, and intercalate into the cathode. The motion of eachlithium ion in the internal circuit of the Li-ion battery is compensatedfor by the motion of an electron in the external circuit, thusgenerating an electric current. The energy density by weight released bythese reactions is both proportional to the potential difference betweenthe two electrodes and to the amount of lithium that will beintercalated into the cathode.

In contrast, when the battery is being charged or re-charged, theopposite process occurs. That is, when an electron moves in the oppositedirection in the external circuit (from the power source charging thebattery) lithium ions deintercalate from the cathode, migrate throughthe ion-conducting electrolyte, and intercalate into the siliconnanoparticles 106 of the anode, causing the silicon nanoparticles 106 toswell or expand.

Again, owing to the structure of the anodes described herein, it ispossible for the charge-cycling process to be repeated numerous timeswith minimal or no strain on the anode.

An exemplary anode structure and process for making the anode structurewill now be described. In this particular embodiment, the dendriticparticle 104 is formed from carbon black nanoparticles that have beenjoined together. Alternatively, commercially available dendritic Cparticles may be used. Annealing the carbon black nanoparticles servesto increase the purity of the carbon, which in turn serves to increasethe cycle life of the anode. Carbon black nanoparticles are used in thisembodiment owing to their relatively low cost and level of initialpurity relative to other allotropes of carbon.

Once the dendritic particle 104 including the annealed carbon blacknanoparticles has been formed, silicon nanoparticles 106 are grown onthe surface using chemical vapor deposition (CVD). Specifically, asilane or a chlorosilane precursor composition is decomposed so as todeposit silicon on the surface of the carbon black dendritic particle104. Any defects on the surface of the carbon black dendritic particle104 serve as nucleation sites for the silicon nanoparticle growth. Caremust be taken to minimize the presence of oxygen during growth so as toavoid the formation of large amounts of native oxide on the surface ofthe silicon nanoparticles 106. Once the silicon nanoparticle CVD step iscomplete, the Si—C nanocomposite building block 102 is formed. In analternate embodiment, nanoparticles of a lithium-silicon alloy areformed on the surface of the dendritic particle.

Next, a plurality of the Si—C nanocomposites 102 can be compactedtogether to form a porous composite 100. The shape of the porouscomposite 100 can be maintained by exposing the plurality of compactedSi—C nanocomposites 102 to a carbon CVD step where a layer of carbon isgrown on at least a portion of the various surfaces of thenanocomposites by decomposition of a hydrocarbon precursor. The layer ofcarbon joins the plurality of Si—C nanocomposites together to form aporous composite.

In some cases, the shape of the porous composite 100 can be maintainedby mixing the plurality of compacted Si—C nanocomposites 102 with asacrificial binder. The porous composite 100 can be exposed to a heattreatment in an oxygen-free environment to transform the sacrificialbinder into carbon.

In some embodiments, the surface of porous composite 100 can be coatedwith a Li-ion permeable material, including but not limited to Li-ionpermeable metal oxides, Li-ion permeable metal fluorides, Li-ionpermeable carbon and Li-ion permeable polymers.

In some embodiments, a Li-ion permeable metal oxide layer may be formedon the surface of porous composite. 100. The thickness of such a layermay in the range of 1 to 20 nm. In some embodiments, an aluminum oxidelayer, may be formed on the surface of porous composite 100. In somecases, oxides of other metals that naturally form protective oxidelayers on their surfaces could be used instead of aluminum oxide. Theseinclude, but are not limited to titanium (Ti) oxide, chromium (Cr)oxide, tantalum (Ta) oxide, niobium (Nb) oxide, and others. Depositionof such oxide coatings can be performed using a variety of oxide coatingdeposition techniques, including physical vapor deposition, chemicalvapor deposition, magnetron sputtering, atomic layer deposition,microwave-assisted deposition, wet chemistry, and others.

For example, metal oxide precursors in the form of a water-soluble saltmay be added to the suspension (in water) of the porous composite 100 tobe coated. The addition of a base (e.g., sodium hydroxide or amine)causes formation of a metal (M) hydroxide. Porous composite particlessuspended in the mixture may then act as nucleation sites forM-hydroxide precipitation. Once particles are coated with a shell ofM-hydroxide, they can be annealed in order to convert the hydroxideshell into a corresponding oxide layer that is then well-adhered to theporous composite.

In some embodiments, a Li-ion permeable metal fluoride or metaloxyfluoride layer may be formed on the surface of porous composite 100.Examples of such metal fluoride materials include, but are not limitedto: vanadium fluoride, vanadium oxyfluoride, iron fluoride, ironoxyfluoride, aluminum fluoride, aluminum oxyfluoride, titanium fluoride,titanium oxyfluoride, aluminum fluoride, aluminum oxyfluoride, zincfluoride, zinc oxyfluoride, niobium fluoride, niobium oxyfluoride,tantalum fluoride, tantalum oxyfluoride, nickel fluoride, nickeloxyfluoride, magnesium fluoride, magnesium oxyfluoride, copper fluoride,copper oxyfluoride, manganese fluoride, and manganese oxyfluoride. Thethickness of such a layer may be in the range of about 1 nm to about 20nm.

In some embodiments, a Li-ion permeable carbon layer may be formed onthe surface of porous composite 100. The thickness of such a layer mayin the range of about 1 nm to about 20 nm.

In some embodiments, a Li-ion permeable polymer layer may be formed onthe surface of porous composite 100. The thickness of such a layer mayin the range of 1 to 20 nm. In some embodiments such a polymer layer iselectrically conductive. In other embodiments such a polymer layer iselectrically insulative. Examples of Li-ion permeable polymers includebut are not limited to sulfonated polystyrene grafted fluorinatedethylene propylene, sulfonated inorganic-organic hybrid polymers,partially fluorinated polystyrenes, organically modified layeredphosphonates, polyphenylene, sulfide, poly(ether ketone),polysaccharides, and poly(ethylene glycol), poly(ethylene oxide).

In some embodiments, the surface of porous composite 100 can be coatedwith several (2 or more) different layers of Li-ion permeable materials,including but not limited to Li-ion permeable metal oxides, Li-ionpermeable metal fluorides, Li-ion permeable carbon and Li-ion permeablepolymers.

In some embodiments, the interface between a surface of porous composite100 and the coating layers may contain additional pores. These poreswill provide some volume for Si expansion. In some embodiment, suchpores can be produced using a sacrificial material. For example, asurface of porous composite 100 may be coated first with a polymer,which decomposes upon heating, and then with a metal oxide or a metaloxide precursor. After annealing the sacrificial polymer interlayer maydecompose forming a void between a surface of porous composite 100 and ametal oxide layer.

In another example, a surface of porous composite 100 may be coatedfirst with a polymer, which decomposes upon heating, and then with apolymer which carbonizes (transforms into carbon) upon heating. Afterannealing the sacrificial polymer interlayer may decompose forming avoid between a surface of porous composite 100 and a carbon layer.

In yet another example, a surface of porous composite 100 may be coatedfirst with a sacrificial oxide, which can be dissolved in certainetching chemicals (acids or bases), and then further coated with a layerof carbon. Upon the treatment of the coated composite in the etchingchemicals the oxide layer may dissolve forming voids between the surfaceof the porous composite and a carbon coating layer. In one embodimentsilicon oxide or aluminum oxide can act as such sacrificial oxide layer.

The resulting coated dendritic C—Si particles may be combined to form aporous composite that can be used to form an anode of a battery.

A plurality of porous composites 100 can be assembled together to form amatrix having the desired shape of the anode. The shape of the matrixcan be maintained using any of the techniques described for forming theporous composite 100 from the plurality of the Si—C nanocomposites 102.

In other situations, instead of a porous composite 100, the plurality ofthe dendritic C—Si particles 102 can be compacted together into thefinal desired shape of the anode. Again, the shape of such a bulkcompacted anode body can be maintained using any of the techniquesdescribed for forming the porous composite 100 from the plurality ofdendritic C—Si particles.

In another embodiment, Si may be used as the material used to form thedendritic particles. In this embodiment, dendritic particles of Si maybe formed by pyrolysis (decomposition) of silane (SiH₄) or chlorosilanegases. Silane compounds decompose into silicon particles, whichfuse/sinter together to form dendritic particles that are athree-dimensional, randomly-ordered assembly or agglomerate of the Sinanoparticles. The Si dendritic particles can be formed into a porouscomposite. The porous composite may be formed by exposing a plurality ofdendritic Si particles to a carbon CVD step where a layer of carbon isgrown on at least a portion of the various surfaces of the dendritic Siparticles by decomposition of a hydrocarbon gas precursor. In analternate embodiment, a lithium-silicon alloy may be used to formdendritic particles.

In some embodiments the deposited carbon on the surface of the Sidendritic particles binds the dendritic particles together as adendritic Si—C porous composite that may be used to form an electrode(e.g., an anode) of a battery.

In another embodiment, a porous Si—C composite may be formed using asacrificial binder. In an embodiment, dendritic particles of Si may beformed from silane (SiH₄) or chlorosilane gases. Alternatively,commercially available dendritic Si particles may be used. The dendriticSi particles may be coated with a sacrificial polymer binder, whichtransforms into a conductive carbon layer during thermal annealing in aninert environment. This carbon binds particles together forming adendritic Si—C porous composite.

In some embodiments, the surface of a dendritic Si—C porous compositecan be coated with a Li-ion permeable material, including but notlimited to Li-ion permeable metal oxides, Li-ion permeable metalfluorides, Li-ion permeable carbon and Li-ion permeable polymers.

In some embodiments, a Li-ion permeable metal oxide layer may be formedon the surface of the dendritic Si—C porous composite. The thickness ofsuch a layer may be in the range of about 1 nm to 20 nm. In someembodiments, an aluminum oxide layer, may be formed on the surface ofthe dendritic Si—C porous composite. In some cases, oxides of othermetals that naturally form protective oxide layers on their surfacescould be used instead of aluminum oxide. These include, but are notlimited to titanium (Ti) oxide, chromium (Cr) oxide, tantalum (Ta)oxide, niobium (Nb) oxide, and others. Deposition of such oxide coatingscan be performed using a variety of oxide coating deposition techniques,including physical vapor deposition, chemical vapor deposition,magnetron sputtering, atomic layer deposition, microwave-assisteddeposition, wet chemistry, and others.

For example, metal oxide precursors in the form of a water-soluble saltmay be added to the suspension (in water) of the dendritic Si—C porouscomposite to be coated. The addition of the base (e.g., sodium hydroxideor amine) causes formation of a metal (M) hydroxide. Dendritic Si—Cporous composite particles suspended in the mixture may then act asnucleation sites for M-hydroxide precipitation. Once dendritic Si—Cporous composites are coated with a shell of M-hydroxide, they can beannealed in order to convert the hydroxide shell into a correspondingoxide layer that is then well-adhered to the composite surface.

In some embodiments, a Li-ion permeable metal fluoride or metaloxyfluoride layer may be formed on the surface of a dendritic Si—Cporous composite. Examples of such metal fluoride materials include, butare not limited to: vanadium fluoride, vanadium oxyfluoride, ironfluoride, iron oxyfluoride, aluminum fluoride, aluminum oxyfluoride,titanium fluoride, titanium oxyfluoride, aluminum fluoride, aluminumoxyfluoride, zinc fluoride, zinc oxyfluoride, niobium fluoride, niobiumoxyfluoride, tantalum fluoride, tantalum oxyfluoride, nickel fluoride,nickel oxyfluoride, magnesium fluoride, magnesium oxyfluoride, copperfluoride, copper oxyfluoride, manganese fluoride, and manganeseoxyfluoride. The thickness of such a layer may be in the range of about1 nm to about 20 nm.

In some embodiments, a Li-ion permeable polymer layer may be formed onthe surface of a dendritic Si—C porous composite. The thickness of sucha layer may be in the range of about 1 nm to about 20 nm. In someembodiments such a polymer layer is electrically conductive. In otherembodiments such a polymer layer is electrically insulative. Examples ofLi-ion permeable polymers include but are not limited to sulfonatedpolystyrene grafted fluorinated ethylene propylene, sulfonatedinorganic-organic hybrid polymers, partially fluorinated polystyrenes,organically modified layered phosphonates, polyphenylene sulfide,poly(ether ketone), polysaccharides, poly(ethylene glycol); andpoly(ethylene oxide).

In some embodiments, the surface of a dendritic Si—C porous compositecan be coated with several (2 or more) different layers of Li-ionpermeable materials, including but not limited to Li-ion permeable metaloxides, Li-ion permeable metal fluorides, Li-ion permeable carbon andLi-ion permeable polymers.

In some embodiments, the interface between a surface of a dendritic Si—Cporous composite and the coating layers may contain additional pores.These pores will provide some volume for Si expansion. In someembodiment, such pores can be produced using a sacrificial material. Forexample, a surface of a dendritic Si—C porous composite may be coatedfirst with a polymer, which decomposes upon heating, and then with ametal oxide or a metal oxide precursor. After annealing the sacrificialpolymer interlayer may decompose forming a void between a surface of thedendritic Si—C porous composite and a metal oxide layer. In anotherexample, a surface of the dendritic Si—C porous composite may be coatedfirst with a polymer, which decomposes upon heating, and then with apolymer which carbonizes (transforms into carbon) upon heating. Afterannealing the sacrificial polymer interlayer may decompose forming avoid (or voids) between a surface of the dendritic Si—C porous compositeand a carbon layer. This void will provide space for Si expansion, whilethe surface C layer will inhibit access of the electrolyte solvent tothe Si surface.

In yet another example, a surface of a dendritic Si—C porous compositemay be coated first with a sacrificial oxide, which can be dissolved incertain etching chemicals (acids or bases), and then further coated witha layer of carbon. Upon the treatment of the coated composite in theetching chemicals the oxide layer may dissolve forming voids between thesurface of a composite and a carbon coating layer. In one embodimentsilicon oxide or aluminum oxide can act as such sacrificial oxide layer.

The coated or uncoated dendritic Si—C porous composite may be used toform an anode as previously described.

In some embodiments, a Li-ion permeable material, including but notlimited to Li-ion permeable metal oxides, Li-ion permeable metalfluorides, Li-ion permeable carbon, Li-ion permeable polymers or anycombination thereof, may be formed on the surface of the dendritic Siparticles before forming a dendritic Si—C composite.

In some embodiments, a Li-ion permeable metal oxide layer may be formedon the surface of dendritic Si particles. The thickness of such a layermay be in the range of about 1 nm to 20 nm. In some embodiments, analuminum oxide layer, may be formed on the surface of the dendritic Siparticles. In some cases, oxides of other metals that naturally formprotective oxide layers on their surfaces could be used instead ofaluminum oxide. These include, but are not limited to titanium (Ti)oxide, chromium (Cr) oxide, tantalum (Ta) oxide, niobium (Nb) oxide, andothers. Deposition of such oxide coatings can be performed using avariety of oxide coating deposition techniques, including physical vapordeposition, chemical vapor deposition, magnetron sputtering, atomiclayer deposition, microwave-assisted deposition, wet chemistry, andothers.

For example, metal oxide precursors in the form of a water-soluble saltmay be added to a suspension (in water) of dendritic Si particles to becoated. The addition of a base (e.g., sodium hydroxide or amine) causesformation of a metal (M) hydroxide. Dendritic Si particles suspended inthe mixture may then act as nucleation sites for M-hydroxideprecipitation. Once dendritic Si particles are coated with a shell ofM-hydroxide, they can be annealed in order to convert the hydroxideshell into a corresponding oxide layer that is then well-adhered to thecomposite surface.

In some embodiments, a Li-ion permeable metal fluoride or metaloxyfluoride layer may be formed on the surface of dendritic Siparticles. Examples of such metal fluoride materials include, but arenot limited to: vanadium fluoride, vanadium oxyfluoride, iron fluoride,iron oxyfluoride, aluminum fluoride, aluminum oxyfluoride, titaniumfluoride, titanium oxyfluoride, aluminum fluoride, aluminum oxyfluoride,zinc fluoride, zinc oxyfluoride, niobium fluoride, niobium oxyfluoride,tantalum fluoride, tantalum oxyfluoride, nickel fluoride, nickeloxyfluoride, magnesium fluoride, magnesium oxyfluoride, copper fluoride,copper oxyfluoride, manganese fluoride, and manganese oxyfluoride. Thethickness of such a layer may be in the range of about 1 nm to about 20nm.

In some embodiments, a Li-ion permeable polymer layer may be formed onthe surface of a dendritic Si particles. The thickness of such a layermay be in the range of about 1 nm to about 20 nm. In some embodimentssuch a polymer layer is electrically conductive. In other embodimentssuch a polymer layer is electrically insulative. Examples of Li-ionpermeable polymers include but are not limited to sulfonated polystyrenegrafted fluorinated ethylene propylene, sulfonated inorganic-organichybrid polymers, partially fluorinated polystyrenes, organicallymodified layered phosphonates, polyphenylene sulfide, poly(etherketone), polysaccharides, poly(ethylene glycol), and poly(ethyleneoxide).

In some embodiments, the surface of dendritic Si particles can be coatedwith several (2 or more) different layers of Li-ion permeable materials,including but not limited to Li-ion permeable metal oxides, Li-ionpermeable metal fluorides, Li-ion permeable carbon and Li-ion permeablepolymers.

The dendritic Si-metal oxide coated particles, dendritic Si-metalfluoride coated particles, dendritic Si-metal oxyfluoride coatedparticles, or dendritic Si—C coated particles may be joined using acarbon CVD step where a layer of carbon is grown on at least a portionof the various surfaces of the dendritic Si-coated particles bydecomposition of a hydrocarbon gas precursor. The resulting composite isa dendritic Si-metal oxide-C porous composite, a dendritic Si-metalfluoride-C porous composite, a dendritic Si-metal oxyfluoride porouscomposite, or a dendritic Si—C coated-C porous composite, respectively.

In another embodiment, dendritic Si-metal oxide coated particles,dendritic Si-metal fluoride coated particles, dendritic Si-metaloxyfluoride coated particles, or dendritic Si—C coated particles may bejoined using a sacrificial binder. In an embodiment, dendritic Si-metaloxide coated particles, dendritic Si-metal fluoride coated particles,dendritic Si-metal oxyfluoride coated particles, or dendritic Si—Ccoated particles may be coated with a sacrificial polymer binder, whichtransforms into a conductive carbon layer during thermal annealing in aninert environment. This carbon binds particles together forming adendritic Si-metal oxide-C porous composite, a dendritic Si-metalfluoride-C porous composite, a dendritic Si-metal oxyfluoride porouscomposite, or a dendritic Si—C coated-C porous composite.

In some embodiments, an additional Li-ion permeable layer or multiplelayers may be formed on the surface of the dendritic Si-metal oxideporous composite, dendritic Si-metal fluoride porous composite,dendritic Si-metal oxyfluoride porous composite or dendritic Si—C-coatedporous composite. Such Li-ion permeable additional layers can be: (a)Li-ion permeable metal oxide layer(s). The thickness of such a layer maybe in the range of about 1 nm to 20 nm. In some embodiments, an aluminumoxide layer, may be formed on the surface of the porous composite. Insome cases, oxides of other metals that naturally form protective oxidelayers on their surfaces could be used instead of aluminum oxide. Theseinclude, but are not limited to titanium (Ti) oxide, chromium (Cr)oxide, tantalum (Ta) oxide, niobium (Nb) oxide, and others. Depositionof such oxide coatings can be performed using a variety of oxide coatingdeposition techniques, including physical vapor deposition, chemicalvapor deposition, magnetron sputtering, atomic layer deposition,microwave-assisted deposition, wet chemistry, and others. (b) metalfluoride or metal oxyfluoride. Examples of such metal fluoride materialsinclude, but are not limited to: vanadium fluoride, vanadiumoxyfluoride, iron fluoride, iron oxyfluoride, aluminum fluoride,aluminum oxyfluoride, titanium fluoride, titanium oxyfluoride, aluminumfluoride, aluminum oxyfluoride, zinc fluoride, zinc oxyfluoride, niobiumfluoride, niobium oxyfluoride, tantalum fluoride, tantalum oxyfluoride,nickel fluoride, nickel oxyfluoride, magnesium fluoride, magnesiumoxyfluoride, copper fluoride, copper oxyfluoride, manganese fluoride,and manganese oxyfluoride. The thickness of such a layer may be in therange of about 1 nm to about 20 nm. (c) Li-ion permeable polymer. Thethickness of such a layer may be in the range of about 1 nm to 20 nm.Examples of Li-ion permeable polymers include but are not limited tosulfonated polystyrene grafted fluorinated ethylene propylene,sulfonated inorganic-organic hybrid polymers, partially fluorinatedpolystyrenes, organically modified layered phosphonates, polyphenylenesulfide, poly(ether ketone), polysaccharides, poly(ethylene glycol), orpoly(ethylene oxide), (d) a combination of 2 or more different layers ofLi-ion permeable materials, including but not limited to Li-ionpermeable metal oxides, Li-ion permeable metal fluorides, Li-ionpermeable carbon and Li-ion permeable polymers.

In some embodiments, the interface between a surface of a dendriticSi-metal oxide porous composite, a dendritic Si-metal fluoride porouscomposite, a dendritic Si-metal oxyfluoride porous composite, or adendritic Si—C-coated porous composite and the additional coating layersmay contain additional pores. These pores will provide some volume forSi expansion. In some embodiment, such pores can be produced using asacrificial material. For example, a surface of the composite may becoated first with a polymer, which decomposes upon heating, and thenwith a metal oxide or a metal oxide precursor. After annealing thesacrificial polymer interlayer may decompose forming a void between asurface of porous composite and a metal oxide layer. In another example,a surface of the composite may be coated first with a polymer, whichdecomposes upon heating, and then with a polymer which carbonizes(transforms into carbon) upon heating. After annealing the sacrificialpolymer interlayer may decompose forming a void (or voids) between asurface of the porous composite and a carbon layer. This void willprovide space for Si expansion, while the surface C layer will inhibitaccess of the electrolyte solvent to the Si surface. In yet anotherexample, a surface of the porous composite may be coated first with asacrificial oxide, which can be dissolved in certain etching chemicals(acids or bases), and then further coated with a layer of carbon. Uponthe treatment of the coated composite in the etching chemicals the oxidelayer may dissolve forming voids between the surface of a composite anda carbon coating layer. In one embodiment silicon oxide or aluminumoxide can act as such sacrificial oxide layer.

The coated or uncoated dendritic Si-metal oxide porous composite,dendritic Si-metal fluoride porous composite, dendritic Si-metaloxyfluoride porous composite or dendritic Si—C-coated porous compositemay be used to form an anode as previously described.

In another embodiment, Si nanoparticles (either synthesized orcommercially obtained) may be fused together to from a dendriticparticle using a carbon backbone. Si nanoparticles may be formed bypyrolysis (decomposition) of silane (SiH₄) or chlorosilane gases underconditions that promote the formation of discrete particles. In thisprocess, the Si nanoparticles are placed in a reactor with a hydrocarbongas. The hydrocarbon gas is decomposed to form dendritic particles thatare composed of a mixture of carbon and silicon nanoparticles. In analternate embodiment, a lithium-silicon alloy may be combined with ahydrocarbon gas to form dendritic particles that are composed of amixture of carbon and lithium-silicon alloy nanoparticles.

In some embodiments, a Li-ion permeable material, including but notlimited to Li-ion permeable metal oxides, Li-ion permeable metalfluorides, Li-ion permeable carbon, Li-ion permeable polymers, or anycombination thereof, may be formed on the surface of the dendritic Si—Cparticles before forming a dendritic Si—C composite.

In some embodiments, a Li-ion permeable metal oxide layer may be formedon the surface of dendritic Si—C particles. The thickness of such alayer may be in the range of about 1 nm to 20 nm. In some embodiments,an aluminum oxide layer, may be formed on the surface of the dendriticSi—C particles. In some cases, oxides of other metals that naturallyform protective oxide layers on their surfaces could be used instead ofaluminum oxide. These include, but are not limited to titanium (Ti)oxide, chromium (Cr) oxide, tantalum (Ta) oxide, niobium (Nb) oxide, andothers. Deposition of such oxide coatings can be performed using avariety of oxide coating deposition techniques, including physical vapordeposition, chemical vapor deposition, magnetron sputtering, atomiclayer deposition, microwave-assisted deposition, wet chemistry, andothers.

For example, metal oxide precursors in the form of a water-soluble saltmay be added to a suspension (in water) of dendritic Si—C particles tobe coated. The addition of a base (e.g., sodium hydroxide or amine)causes formation of a metal (M) hydroxide. Dendritic Si—C particlessuspended in the mixture may then act as nucleation sites forM-hydroxide precipitation. Once dendritic Si—C particles are coated witha shell of M-hydroxide, they can be annealed in order to convert thehydroxide shell into a corresponding oxide layer that is thenwell-adhered to the composite surface.

In some embodiments, a Li-ion permeable metal fluoride or metaloxyfluoride layer may be formed on the surface of dendritic Si—Cparticles. Examples of such metal fluoride materials include, but arenot limited to: vanadium fluoride, vanadium oxyfluoride, iron fluoride,iron oxyfluoride, aluminum fluoride, aluminum oxyfluoride, titaniumfluoride, titanium oxyfluoride, aluminum fluoride, aluminum oxyfluoride,zinc fluoride, zinc oxyfluoride, niobium fluoride, niobium oxyfluoride,tantalum fluoride, tantalum oxyfluoride, nickel fluoride, nickeloxyfluoride, magnesium fluoride, magnesium oxyfluoride, copper fluoride,copper oxyfluoride, manganese fluoride, and manganese oxyfluoride. Thethickness of such a layer may be in the range of about 1 nm to about 20nm.

In some embodiments, a Li-ion permeable polymer layer may be formed onthe surface of a dendritic Si—C particles. The thickness of such a layermay be in the range of about 1 nm to about 20 nm. In some embodimentssuch a polymer layer is electrically conductive. In other embodimentssuch a polymer layer is electrically insulative. Examples of Li-ionpermeable polymers include but are not limited to sulfonated polystyrenegrafted fluorinated ethylene propylene, sulfonated inorganic-organichybrid polymers, partially fluorinated polystyrenes, organicallymodified layered phosphonates, polyphenylene sulfide, poly(etherketone), polysaccharides, poly(ethylene glycol), and poly(ethyleneoxide).

In some embodiments, the surface of dendritic Si—C particles can becoated with several (2 or more) different layers of Li-ion permeablematerials, including but not limited to Li-ion permeable metal oxides,Li-ion permeable metal fluorides, Li-ion permeable carbon and Li-ionpermeable polymers.

The dendritic Si—C-metal oxide coated particles, dendritic Si—C-metalfluoride coated particles, dendritic Si—C-metal oxyfluoride coatedparticles, or dendritic Si—C—C coated particles may be joined using acarbon CVD step where a layer of carbon is grown on at least a portionof the various surfaces of the dendritic Si-coated particles bydecomposition of a hydrocarbon gas precursor. The resulting composite isa dendritic Si—C-metal oxide porous composite, a dendritic Si—C-metalfluoride porous composite, a dendritic Si—C-metal oxyfluoride porouscomposite, or a dendritic Si—C coated porous composite, respectively.

The coated dendritic Si—C particles may then be formed into a porouscomposite. The porous composite may be formed by exposing a plurality ofcoated dendritic Si—C particles to a carbon CVD step having operatingconditions selected to promote growth of a layer of carbon on at least aportion of the various surfaces of the coated dendritic Si—C particlesby decomposition of a hydrocarbon gas precursor. The deposited carbon onthe surface of the coated dendritic Si—C particles binds the coateddendritic Si—C particles together to form a coated dendritic Si—C porouscomposite that may be used to form an electrode (e.g., an anode) of abattery. In another embodiment, the coated dendritic Si—C particles maybe coated with a sacrificial polymer binder, which transforms into aconductive carbon layer during thermal annealing in an inertenvironment. This carbon binds particles together forming a coateddendritic Si—C porous composite

In some embodiments, an additional Li-ion permeable layer or multiplelayers may be formed on the surface of the dendritic Si—C-metal oxideporous composite, dendritic Si—C-metal fluoride porous composite,dendritic Si—C-metal oxyfluoride porous composite or dendriticSi—C-coated porous composite. Such Li-ion permeable additional layerscan be: (a) Li-ion permeable metal oxide layer(s). The thickness of sucha layer may be in the range of about 1 nm to 20 nm. In some embodiments,an aluminum oxide layer, may be formed on the surface of the porouscomposite. In some cases, oxides of other metals that naturally formprotective oxide layers on their surfaces could be used instead ofaluminum oxide. These include, but are not limited to titanium (Ti)oxide, chromium (Cr) oxide, tantalum (Ta) oxide, niobium (Nb) oxide, andothers. Deposition of such oxide coatings can be performed using avariety of oxide coating deposition techniques, including physical vapordeposition, chemical vapor deposition, magnetron sputtering, atomiclayer deposition, microwave-assisted deposition, wet chemistry, andothers. (b) metal fluoride or metal oxyfluoride. Examples of such metalfluoride materials include, but are not limited to: vanadium fluoride,vanadium oxyfluoride, iron fluoride, iron oxyfluoride, aluminumfluoride, aluminum oxyfluoride, titanium fluoride, titanium oxyfluoride,aluminum fluoride, aluminum oxyfluoride, zinc fluoride, zincoxyfluoride, niobium fluoride, niobium oxyfluoride, tantalum fluoride,tantalum oxyfluoride, nickel fluoride, nickel oxyfluoride, magnesiumfluoride, magnesium oxyfluoride, copper fluoride, copper oxyfluoride,manganese fluoride, and manganese oxyfluoride. The thickness of such alayer may be in the range of about 1 nm to about 20 nm. (c) Li-ionpermeable polymer. The thickness of such a layer may be in the range ofabout 1 nm to 20 nm. Examples of Li-ion permeable polymers include butare not limited to sulfonated polystyrene grafted fluorinated ethylenepropylene, sulfonated inorganic-organic hybrid polymers, partiallyfluorinated polystyrenes, organically modified layered phosphonates,polyphenylene sulfide, poly(ether ketone), polysaccharides,poly(ethylene glycol), or poly(ethylene oxide). (d) a combination of 2or more different layers of Li-ion permeable materials, including butnot limited to Li-ion permeable metal oxides, Li-ion permeable metalfluorides, Li-ion permeable carbon and Li-ion permeable polymers.

In some embodiments, the interface between a surface of a dendriticSi—C-metal oxide porous composite, a dendritic Si—C-metal fluorideporous composite, a dendritic Si—C-metal oxyfluoride porous composite,or a dendritic Si—C—C-coated porous composite and the additional coatinglayers may contain additional pores. These pores will provide somevolume for Si expansion. In some embodiment, such pores can be producedusing a sacrificial material. For example, a surface of the compositemay be coated first with a polymer, which decomposes upon heating, andthen with a metal oxide or a metal oxide precursor. After annealing thesacrificial polymer interlayer may decompose forming a void between asurface of porous composite and a metal oxide layer. In another example,a surface of the composite may be coated first with a polymer, whichdecomposes upon heating, and then with a polymer which carbonizes(transforms into carbon) upon heating. After annealing the sacrificialpolymer interlayer may decompose forming a void (or voids) between asurface of the porous composite and a carbon layer. This void willprovide space for Si expansion, while the surface C layer will inhibitaccess of the electrolyte solvent to the Si surface. In yet anotherexample, a surface of the porous composite may be coated first with asacrificial oxide, which can be dissolved in certain etching chemicals(acids or bases), and then further coated with a layer of carbon. Uponthe treatment of the coated composite in the etching chemicals the oxidelayer may dissolve forming voids between the surface of a composite anda carbon coating layer. In one embodiment silicon oxide or aluminumoxide can act as such sacrificial oxide layer.

The coated or uncoated dendritic Si—C-metal oxide porous composite,dendritic Si—C-metal fluoride porous composite, dendritic Si—C-metaloxyfluoride porous composite or dendritic Si—C-coated porous compositemay be used to form an anode as previously described.

It will be appreciated that in the concept of the invention thedisclosed nanoparticles 106 can be produced not only of Si but also froma variety of other higher capacity anode materials that exhibitsignificant (greater than 10%) volume changes during insertion andextraction of Li ions. Examples of such materials include: (i) heavily(and “ultra-heavily”) doped silicon; (ii) group IV elements; (iii)binary silicon alloys (or mixtures) with metals; (iv) ternary siliconalloys (or mixtures) with metals; and (v) other metals and metal alloysthat form alloys with lithium.

Heavily and ultra-heavily doped silicon include silicon doped with ahigh content of Group III elements, such as boron (B), aluminum (Al),gallium (Ga), indium (In), or thallium (Tl), or a high content of GroupV elements, such as nitrogen (N), phosphorus (P), arsenic (As), antimony(Sb), or bismuth (Bi). By “heavily doped” and “ultra-heavily doped,” itwill be understood that the content of doping atoms is typically in therange of 3,000 parts per million (ppm) to 700,000 ppm, or approximately0.3% to 70% of the total composition.

Group IV elements used to form higher capacity anode materials mayinclude Ge, Sn, Pb, and their alloys, mixtures, or composites, with thegeneral formula of Si_(a)—Ge_(b)—Sn_(e)—Pb_(a)—C_(e)-D_(f), where a, b,c, d, e, and f may be zero or non-zero, and where D is a dopant selectedfrom Group III or Group V of the periodic table.

For binary silicon alloys (or mixtures) with metals, the silicon contentmay be in the range of approximately 20% to 99.7%. Examples of such asalloys (or mixtures) include, but are not limited to: Mg—Si, Ca—Si,Sc—Si, Ti—Si, V—Si, Cr—Si, Mn—Si, Fe—Si, Co—Si, Ni—Si, Cu—Si, Zn—Si,Sr—Si, Y—Si, Zr—Si, Nb—Si, Mo—Si, Tc—Si, Ru—Si, Rh—Si, Pd—Si, Ag—Si,Cd—Si, Ba—Si, Hf—Si, Ta—Si, and W—Si. Such binary alloys may be doped(or heavily doped) with Group III and Group V elements. Alternatively,other Group IV elements may be used instead of silicon to form similaralloys or mixtures with metals. A combination of various Group IVelements may also used to form such alloys or mixtures with metals.

For ternary silicon alloys (or mixtures) with metals, the siliconcontent may also be in the range of approximately 20% to 99.7%. Suchternary alloys may be doped (or heavily doped) with Group III and GroupV elements. Other Group IV elements may also be used instead of siliconto form such alloys or mixtures with metals. Alternatively, other GroupIV elements may be used instead of silicon to form similar alloys ormixtures with metals. A combination of various Group IV elements mayalso used to form such alloys or mixtures with metals.

In some embodiment, during CVD deposition processing, the composition ofthe coating may be altered by adding doping gas to the gas used to formthe deposited layer. Specific examples of doping gases that may be addedto any of the CVD processes described herein include, but are notlimited to, ammonia (NH₃), diborane (B₂H₆), or phosphine (PH₃). Thesegases may be combined with hydrocarbon or silane gases in CVD depositionprocesses to alter the physical properties of the formed layer ornanoparticles.

In some embodiments, a porous composite, as described herein, mayfurther include lithium. Lithium may be in the form of lithium ions thatare associated with one or more components of the porous composite. Inan embodiment, lithium may be incorporated into the dendritic particles.For example, the dendritic particles may be a three-dimensional,randomly-ordered assembly of nanoparticles of carbon having lithiumincorporated into the dendritic particles. In some embodiments, a porouscomposite may be composed of the dendritic particles that includenanoparticles of carbon having lithium incorporated into the dendriticparticles, and a plurality of discrete non-porous nanoparticles of anon-carbon Group 4A element or mixture thereof alloyed with lithium anddisposed on a surface of the lithium incorporated dendritic particle.

In another embodiment, a porous composite may include dendriticparticles that are composed of lithium-silicon alloy nanoparticles. Inan alternate embodiment, a porous composite may include dendriticparticles that are composed of lithium-silicon alloy nanoparticles in acarbon matrix. In yet another alternate embodiment, a porous compositemay include dendritic particles that are composed of lithium-siliconalloy nanoparticles in a lithium-containing carbon matrix.

Alternatively, the dendritic particles may be formed as has beenpreviously described. Prior to forming the porous composite, thedendritic particles may be treated with a lithium ion containingelectrolyte to incorporate lithium ions into the dendritic particles.The lithiated dendritic particles may be used to form a porous compositethat is pre-lithiated. In another embodiment, dendritic particles,formed as has been previously described, may be joined to form a porouscomposite. Prior to use of the porous composite to form an electrode,the porous composite may be treated with a lithium ion containingelectrolyte to incorporate lithium ions into the porous composite. Thelithiated porous composite may be used to form an electrode that ispre-lithiated.

Alternatively, lithium can be incorporated into the dendritic particlesor lithium-ion permeable coating during chemical synthesis. Thelithiated dendritic particles may be used to form a porous compositethat is pre-lithiated. In another embodiment, lithium containing andlithium-ion permeable coating may formed on the surface of pre-lithiateddendritic particles or on the surface of a pre-lithiated porouscomposite. The lithiated porous composite may be used to form anelectrode that is pre-lithiated.

In some embodiments, lithium may be incorporated into a lithium ionpermeable polymer layer that is formed over the dendritic particlesand/or the porous composite. In one embodiments, a lithium ion permeablepolymer that includes lithium (e.g. lithium ions) may be formed over atleast a portion of the dendritic particles of the porous composite. Inan embodiment, a lithium ion permeable polymer that includes lithium(e.g., lithium ions) may be formed over at least a portion of the porouscomposite. The lithium containing polymer may be formed prior tocoating, during coating, or after coating of the dendritic particles orthe porous composite.

In some embodiments, lithium may be incorporated into a lithium ionpermeable ceramic layer that is formed over the dendritic particlesand/or the porous composite. In one embodiments, a lithium ion permeableceramics that includes lithium (e.g. lithium ions) may be formed over atleast a portion of the dendritic particles of the porous composite. Inan embodiment, a lithium ion permeable ceramics that includes lithium(e.g., lithium ions) may be formed over at least a portion of the porouscomposite. The lithium containing ceramics may be formed prior tocoating, during coating, or after coating of the dendritic particles orthe porous composite. In some embodiments, a lithium ion permeableceramic layer may compose metal oxide, metal fluoride or metaloxyfluoride. In some embodiments, a lithium ion permeable ceramic layermay compose one none-lithium metal. In some embodiments, a lithium ionpermeable ceramic layer may compose two none-lithium metals.

In some embodiments, lithium may be incorporated into a lithium ionpermeable coating composed of a combination of 2 or more differentlayers of Li-ion permeable materials, including but not limited toLi-ion permeable metal oxides, Li-ion permeable metal fluorides, Li-ionpermeable metal oxyfluorides, Li-ion permeable carbon and Li-ionpermeable polymers. In some embodiments, lithium may be incorporatedinto all the layers of a multi-layered lithium ion permeable coating.

The following examples are included to demonstrate preferred embodimentsof the invention. It should be appreciated by those of skill in the artthat the techniques disclosed in the examples which follow representtechniques discovered by the inventor to function well in the practiceof the invention, and thus can be considered to constitute preferredmodes for its practice. However, those of skill in the art should, inlight of the present disclosure, appreciate that many changes can bemade in the specific embodiments which are disclosed and still obtain alike or similar result without departing from the spirit and scope ofthe invention.

Example 1

Fabrication and Characterization of Si—C Composite Anode Material

In this example, a hierarchical “bottom-up” approach was used to formSi—C porous composite granules with high capacity, stable performance,and particle size comparable to that of milled graphite (i.e., about 15to about 30 micrometers). This powder size is commonly used in theproduction of Li-ion battery electrodes and does not possess the sameinhalation hazard as nanoparticles. This “bottom-up” approach allowedfor the fabrication of high capacity stable composite anodes with rapidcharging capability.

Briefly, a chemical vapor deposition (CVD) synthesis process has beendesigned for depositing Si nanoparticles on the surface of carbon black(CB) nanoparticles, wherein the CB nanoparticles form short dendriticchains during high temperature pre-annealing. The about 500 nm to about1 μm multi-branched nanocomposite was then self-assembled into largeporous spherical granules during the atmospheric pressure CVD depositionof C (as schematically shown in FIG. 2). The Si CVD deposition time aswell as the pressure and temperature in the deposition system determinedthe size of the deposited Si nanoparticles. The size of the branches inthe dendritic particle and the size of the deposited Si nanoparticlesdetermined the pore size in the granule. The diameter of the compositegranules was influenced by the carbon CVD process parameters and by thesize of the initial branched carbon dendritic particles. Therefore, thedeveloped process allowed control over the particle size, pore size, andcomposition of the composite granule.

Annealed and chained CB particles were selected as substrates for Sispheres assembly due to their open structure, very low apparent density,and high specific surface area (about 80 m²/g), providing multipleaccessible sites for Si deposition. The ultra low cost of carbon black(about 10 to about 20% of the cost of purified natural graphite) andlarge production volume (about 9 times higher than that of naturalgraphite) help maintain the low cost of the synthesized compositegranules. Impurities in carbon electrodes are detrimental to batteryoperation, contributing to parasitic side reactions, gassing in thecells, self-discharge and degradation of the shelf life of the cells.The annealing of CB at temperatures above about 2000° C. resulted ingraphitization, linkage of neighboring particles, and a very high degreeof purification (greater than about 99.9%), promoting consistentproperties, which are desired for Li-ion battery systems and areunattainable via chemical purification with acids.

Si deposition onto the annealed carbon black (˜0.5 g) was carried out at.about.1 torr in a horizontal tube furnace (inner-tube diameter˜28 mm)heated to 500 C. High-purity 5% SiH₄ in a He precursor gas mixture(Airgas) was introduced at a flow rate of 50 sccm for 1 h. Before andafter the Si deposition experiments, the system was purged withhigh-purity Ar (99.99%, Airgas) at a flow rate of 50 sccm. The sampleswere taken out of the furnace at temperatures below 50 C.

Transmission electron microscopy (TEM) revealed the nanoparticles topossess a spherical shape of about 10 nm to about 30 nm in diameter,having been deposited on the surface of the annealed CB (FIG. 3(a)), aspreviously shown in FIG. 1(a). The black arrows in FIG. 3(a) point tospherical amorphous Si nanoparticles, while white arrows point to theedges of the graphitized carbon black backbone chain of the dendriticparticle (the size of the inset is 800×800 nm). Most nanoparticlesexhibited an amorphous microstructure or were highly disordered, asshown in FIG. 3(b). The nanoparticles densely coated the carbon surface,frequently attached to the edges of the graphitic structures. Once astable nucleus was formed, growth occurred via adsorption of gas specieson the nucleus surface. The spherical shape of the particles minimizedthe contact area between the Si and CB surfaces, likely due to the highinterfacial energy between Si and the flat faces of the graphitized CBparticles, which possessed a negligible concentration of surfacefunctionalities. The TEM image of FIG. 3(c) shows the highly-orderedgraphitic structure of a carbon black surface with (002) interplanarspacing of about 3.34 Angstroms and the amorphous structure of the Sinanoparticles. The low synthesis temperature may have minimized thesurface mobility of Si atoms and contributed to the smooth morphology ofthe Si surface. No impurities were detected in the sample by energydispersive X-ray spectroscopy (EDX), as shown in FIG. 3(d).

In wet granulation, a liquid binder wets small primary particles as theyare agitated, causing them to self-assemble into larger spheres by acombination of viscous and capillary forces. The drying or annealingprocess transforms the binder into a dense solid which preserves theshape of the granules. For electrode particles, the solid granule shouldideally have high electrical conductivity, high mechanical stability,and high permeability to Li ions. Graphitic carbon exhibits a uniquecombination of these attributes. In order to prevent the oxidation of Sinanoparticles a hydrocarbon was selected as a carbon-precursor binderfor granulation. In a conventional wet granulation process, a liquidbinder is typically introduced as droplets. It penetrates into the poresof the powder surface, forming initial nuclei, which grow over time. Ifthe droplet size is relatively small, the nucleation will occur bydistribution of the drops on the surface of the particles and subsequentparticle coalescence. The process is similar to melt agglomeration,where the binder melts and the melt-coated particles stick together toform granules. However, it is commonly difficult to achieve uniformbinder deposition required for the controlled and uniform formation ofgranules. Therefore, in this study, the binder was introduced in gaseousform.

Carbon deposition was carried out at atmospheric pressure in ahorizontal tube furnace (inner-tube diameter×20 mm) heated to 700 C.High-purity C₃H₆ (propylene) precursor gas (99.5%, Airgas) wasintroduced at a flow rate of 50 sccm for 30 min. A bubbler filled withmineral oil was placed at the exhaust to minimize the backflow of airinto the system. Before and after the C deposition experiments, thesystem was purged with high-purity Ar (99.99%, Airgas) at a flow rate of50 sccm. The samples were taken out of the furnace at temperatures below50 C. This higher temperature step caused significant crystallization inthe deposited Si nanoparticles. X-ray diffraction (XRD) analysis of theproduced samples showed the average grain size of the Si nanoparticlesto be about 30 nm, as shown in FIG. 3(e). TEM studies confirmed thecrystalline structure of Si nanoparticles after exposure to about 700°C. (FIG. 3(f)).

The SEM micrographs of FIGS. 4(a) and (b) show the spherical granulesformed in the course of carbon deposition. The particle surface wasrough, with surface asperities of about 500 nm to about 1 as seen inFIGS. 4(b) and (c). In spite of the carbon coating, small Sinanoparticles were visible on the surface, as evidenced in FIG. 4(d).The white arrows in FIG. 4(d) point to carbon-coated Si nanoparticlesvisible on the surface of the granules. The diameter of the granulespheres ranged from about 15 m to about 35 μm and showed a narrowparticle size distribution with the average diameter of about 26 μm(FIG. 4(e)). The granule size distribution was controlled by thegranulation process conditions, as shown in FIG. 6 and could beoptimized for the specific application. Propylene decomposition tookplace via multiple intermediate steps. The hydrocarbon products ofintermediate steps of C₃H₆ decomposition are known to form largermolecular weight compounds, including toluene, ethylbenzene, styrene,naphthalene, biphenyl and others, which adsorb on the surface of thesubstrates during the CVD reaction. In the adsorbed state, they acted asa liquid agglomeration binder before their final transformation intocarbon. Initially, vibration was introduced to the sample tube in orderto agitate the nanoparticles. However, further experiments proved thatdue to the very low density of the granules, the vibration wasunnecessary. All of the granules were synthesized without artificialagitation in a simple horizontal tube furnace.

The bottom-up assembly preserved most of the surface area of the primaryparticles. Indeed, N₂ gas sorption measurements, as shown in FIG. 4(f)showed that the decrease of the specific surface area (SSA) after carbondeposition was rather modest—Brunauer-Emmett-Teller (BET) SSA of theSi—C self-assembled granules was about 24 m²/g, which was close to thatof the Si-decorated CB (about 33 m²/g). The pore size distribution ofthe spherical particles showed the presence of about 30 nm to about 100nm pores (FIG. 4(g)). These pores were also visible on the SEMmicrographs shown in FIGS. 4(c) and (d). Carbon coating of the surfaceof the pure CB also resulted in the formation of porous granules withlarger surface features and no visible particles of about 10 nm to about30 nm diameter (FIG. 4(h)).

Example 2

Fabrication and Characterization of Coin Cells Using Si—C CompositeAnode

Coin cells (2016) with metallic Li counter electrodes were employed toevaluate the electrochemical performance of the anodes produced inEXAMPLE 1. Working electrodes were prepared by casting slurry containingan active material (C—Si composite granules or graphite or annealedcarbon black), a polyvinylidene fluoride binder (pure 9305 (Kureha) forcarbon electrodes and 9305 with 10 wt % addition of polyacrylic acid forSi-containing electrodes; 20 wt % of the binder was used for annealedcarbon black and for C—Si composite granules and 10 wt % for graphite)and N-methyl-2-pyrrolidone on an 18 μm Cu foil (Fukuda). The electrodeswere calendared and degassed in vacuum at 70 C for at least 2 h insidean Ar-filled glove box (<1 ppm of oxygen and water, InnovativeTechnology) and were not exposed to air before assembling into thecells. The commercial electrolyte was composed of 1M LiPF₆ salt in anethylene carbonate/diethyl carbonate/dimethyl carbonate/vinylenecarbonate mixture (Novolyte Technologies). Lithium metal foil (1 mmthick) was used as a counter electrode. 2016 stainless-steel coin cells(without any springs) were used for electrochemical measurements. Theworking electrode foil was spot-welded to the coin cell for improvedelectrical contact. The charge and discharge rates were calculatedassuming the theoretical capacities for C and Si, given the compositionof the active material (either C or C—Si mixture). The coulombicefficiency was calculated as 100% (C^(dealloy)=C^(alloy)), whereC^(alloy) and C^(dealloy) are the capacity of the anodes for Liinsertion and extraction.

FIG. 5(a) illustrates the reversible Li deintercalation capacity andCoulombic efficiency of the granule electrodes vs. cycle number incomparison to the theoretical capacity of graphite. The specificreversible deintercalation capacity of the sample with an estimatedabout 50 wt. % of Si reached about 1950 mAh/g at C/20, as shown in FIG.5(a). This gravimetric capacity was greater than about 5 times higherthan that of the theoretical capacity of graphite, about 6 times that ofhigh performance graphitic anodes, and was about 16 times that of theannealed carbon black (FIGS. 5(a), 5(b) and 7). The specific capacity ofthe Si nanoparticles alone was estimated to be about 3670 mAh/g at C/20,which is the highest value ever reported for nanoparticles. Itapproached the theoretical capacity of Si (about 4200 mAh/g if Li₂₂Si₅is achieved). Such high specific capacity value indicates highaccessibility of the active Si for Li insertion in the designedcomposite architecture. The overall carbon contribution was estimated tobe about 230 mAh/g (115 mAh/0.5 g). The volumetric capacity wasdetermined to be about 1270 mAh/cc at C/20, which was higher than about620 mAh/g for graphitic anodes. The irreversible capacity losses in thefirst cycle (FIG. 5(a)) are related to the solid-electrolyte interphaseformation and, in contrast to carbon black (FIGS. 5(b) and 7), arerather modest (about 15%) due to the high electrode capacity (FIG.4(g)).

While Si anodes are known to suffer from sluggish kinetics, theself-assembled electrodes of EXAMPLE 1 demonstrated outstanding highrate capability. The specific capacity of the composite anodes at thefast discharge rates of 1 C and 8 C was 1590 and 870 mAh/g,respectively, which was about 82 and about 45% of that at C/20 (FIGS.5(a) and (b)). Even graphite, with high Li diffusion coefficients andlow overall capacity could not match such capacity retention at 8 C rate(2.98 A/g) and showed deintercalation capacity of about 40 mAh/g, whichwas 13% of the C/20 specific capacity (FIG. 5(b)). For the same specificcurrent value (2.98 A/g), the composite Si—C electrodes of EXAMPLE 1showed capacity in excess of 1500 mAh/g, which was over 37 times higher.Clearly, in spite of the large particle size (FIGS. 4(a) and (b)), Liions were able to rapidly reach the active anode material within eachgranule.

The differential capacity curves of FIG. 5(c) show broad lithiation (Liinsertion) peaks at 0.21 and 0.06 V, and a narrower delithiation (Liextraction) peak at 0.5 V. The C delithiation peaks commonly observed at0.2V were too small to be visible, due to the very small contribution ofcarbon to the overall anode capacity. A delithiation peak at 0.3 V oftenreported in both micron-scale Si-powder and Si-nanowire cells was notpresent. An increase in the 0.5 V peak height after the first cycleindicates improvement in Li extraction kinetics. The formation of anamorphous S—Li alloy upon the insertion of Li into crystalline Si in thefirst cycle began at 0.1 V, in agreement with previous studies onnanowires. Subsequent cycles showed an additional lithiation peak at0.21 V, which corresponds to higher voltage lithiation of amorphous S—Liphase.

The pores available in the composite granules for Si expansion during Liinsertion (FIGS. 4(c), (d), (f), and (g)) also allowed for efficient andstable anode performance (FIG. 5(a)). The SEM studies of the anodeparticles after high speed mixing, calendaring, and cycling demonstratedexceptional robustness of the granules (FIG. 5(d)). The tap density ofthe Si—C powder was estimated to be about 0.49 g/cc, which is lower thanthat of the graphite (about 1.3 g/cc), but higher than that of annealedcarbon black (about 0.22 g/cc). The Si nanopowder (10-30 nm) alone wasexpected to have an even lower tap density.

The observed high capacity (FIG. 5(a)), combined with excellent samplestability and high rate capability was unprecedented in Si—C compositepowders. In contrast to many photonic, electronic, or membraneapplications, where a high degree of order is typically required, thegranules assembled according to EXAMPLE 1 may benefit from a disorder intheir structure. If the path of Li-ions is blocked or impeded in onenarrow channel by an expanded Si—Li alloy particle or by an area ofunevenly formed solid-electrolyte interphase (SEI), the interconnectedaperiodic porous network allowed for the redirection of the ion traffic,maintaining rapid charging capability for these granules. Therefore, thedisorder in the granules may enhance the functionality of the compositeanode, as it does in some photonic crystals and catalytic structures.

Thus, these two examples demonstrated applications of a hierarchicalbottom-up assembly method for the rational design of nanocompositepowders that offer exceptional properties for use in energy storageapplications. While nanoparticles or nano-whiskers are known to possessinhalation and often explosion risks, poor flow and handling, andchallenges in metering and control, the Si—C nanocomposite granules ofthese examples provide improved handling, reduced dustiness whichminimizes losses, increased bulk density, and other positive attributes.

Further modifications and alternative embodiments of various aspects ofthe invention will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as examples of embodiments. Elements and materials maybe substituted for those illustrated and described herein, parts andprocesses may be reversed, and certain features of the invention may beutilized independently, all as would be apparent to one skilled in theart after having the benefit of this description of the invention.Changes may be made in the elements described herein without departingfrom the spirit and scope of the invention as described in the followingclaims.

What is claimed is:
 1. A composite particle, comprising: anelectrically-conductive matrix having a three-dimensional structurecomprising pores; and a plurality of silicon nanoparticles at leastpartially disposed within the electrically-conductive matrix, wherein: acontent of silicon in the composite particle is in a range of about 15wt. % to about 90 wt. %; the pores comprise pores with widths in a rangeof about 1 nm to about 100 nm; and the pores define a pore volume thatis different from a volume that is occupied by the plurality of siliconnanoparticles.
 2. The composite particle of claim 1, wherein one or moreof the plurality of silicon nanoparticles comprise silicon, one or moreoxides of silicon, or a combination thereof.
 3. The composite particleof claim 1, wherein the electrically-conductive matrix comprises carbon.4. The composite particle of claim 3, wherein theelectrically-conductive matrix comprises carbon.
 5. The compositeparticle of claim 1, wherein the one or more of the plurality of siliconnanoparticles are formed by decomposition of a silane or a chlorosilaneat an elevated temperature.
 6. The composite particle of claim 5,wherein the silane or the chlorosilane comprises SiH₄.
 7. The compositeparticle of claim 1, wherein one or more of the plurality of siliconnanoparticles are nonporous.
 8. The composite particle of claim 1,wherein one or more of the plurality of silicon nanoparticles arespherical.
 9. The composite particle of claim 1, wherein one or more ofthe plurality of silicon nanoparticles are doped with one or moreelements selected from the group: nitrogen (N), boron (B), phosphorus(P), nitrogen (N), aluminum (Al) and lithium (Li).
 10. The compositeparticle of claim 1, wherein: the composite particle is at leastpartially coated with a Li-ion permeable material to inhibit access ofelectrolyte solvent to the plurality of silicon nanoparticles disposedwithin the electrically-conductive matrix.
 11. The composite particle ofclaim 10, wherein: the Li-ion permeable material encases an outersurface of the composite particle.
 12. The composite particle of claim10, wherein: the Li-ion permeable material comprises carbon.
 13. Thecomposite particle of claim 12, wherein: the carbon comprises chemicalvapor deposition (CVD)-deposited carbon.
 14. The composite particle ofclaim 13, wherein: the CVD-deposited carbon is formed by decompositionof a hydrocarbon precursor.
 15. The composite particle of claim 14,wherein: the hydrocarbon precursor comprises propylene (C₃H₆).
 16. Thecomposite particle of claim 10, wherein: the Li-ion permeable materialcomprises a metal oxide.
 17. The composite particle of claim 16,wherein: the metal oxide comprises one or more metals selected from:aluminum (Al), titanium (Ti), chromium (Cr), tantalum (Ta) and niobium(Nb)
 18. The composite particle of claim 10, wherein: the Li-ionpermeable material comprises a polymer.
 19. The composite particle ofclaim 18, wherein: the polymer comprises one or more of the following:sulfonated polystyrene, sulfonated inorganic-organic hybrid polymers,phosphonates, polyphenylene, poly(ether ketone), polysaccharides,poly(ethylene glycol) and poly(ethylene oxide).
 20. The compositeparticle of claim 10, wherein: the Li-ion permeable material comprisestwo or more layers with distinct compositions and/or properties.
 21. Thecomposite particle of claim 1, wherein the composite particle has a sizein a range of about 100 nanometers to about 40 micrometers, or whereinthe composite particle has a Brunauer-Emmett-Teller (BET) specificsurface area that is less than or equal to about 24 m²/g, or acombination thereof.
 22. The composite particle of claim 1, wherein atotal pore volume of the composite particle is less than about 20 timesthe volume occupied by the plurality of silicon nanoparticles.
 23. Thecomposite particle of claim 1, wherein the composite particle isspherical or substantially spherical.
 24. The composite particle ofclaim 1, wherein: the composite particle exhibits a reversiblelithiation capacity in a range from about 870 mAh/g to about 1950 mAh/gduring Li-ion battery operation.
 25. A battery electrode composition,comprising: a plurality of composite particles that each correspond tothe composite particle of claim 1; an electrically conductive additive;and a polymeric binder.
 26. The battery electrode composition of claim25, wherein: the polymeric binder comprises an acrylic polymer.
 27. Thebattery electrode composition of claim 26, wherein the acrylic polymercomprises a polyacrylic acid.
 28. The battery electrode composition ofclaim 25, wherein: the electrically conductive additive comprisescarbon.
 29. The battery electrode composition of claim 28, wherein: thecarbon comprises carbon black.
 30. A Li-ion battery, comprising: acurrent collector comprising Cu; an anode formed on the currentcollector and comprising the battery electrode composition of claim 25;a cathode; and an electrolyte interposed between the anode and thecathode, wherein the electrolyte comprises LiPF₆ salt and a solventcomposition comprising vinylene carbonate (VC).